Latches inside: Reverse-engineering the Intel 8086's instruction register (righto.com)

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The Intel 8086 microprocessor is one of the most influential chips ever created; it led to the x86 architecture that dominates desktop and server computing today. But it is still simple enough that its circuitry can be studied under the microscope and understood. In this post, I explain the implementation of a dynamic latch, a circuit that holds a single bit. The 8086 has over 80 latches scattered throughout the chip, holding a variety of important processor state bits,1 but I’ll focus on the eight latches that implement the instruction register and hold the instruction that is being executed.

How flip-flops are implemented in the Intel 8086 processor (righto.com) A key concept for a processor is the management of “state”, information that persists over time. Much of a computer is built from logic gates, such as NAND or NOR gates, but logic gates have no notion of time. Processors also need a way to hold values, along with a mechanism to move from step to step in a controlled fashion. This is the role of “sequential logic”, where the output depends on what happened before. Sequential logic usually operates off a clock signal,1 a sequence of regular pulses that controls the timing of the computer. (If you have a 3.2 GHz processor, for instance, that number is the clock frequency.)